1. Field of the Invention
This invention relates to a bag having a unique closure of simple, yet highly effective, construction which has numerous advantages including: use of a cost-saving flush cut tube as opposed to expensive stepped cut tubes, high strength at the region of closure, prevention of sifting, ability to be butt printed, the capability to be valved without extensive modification, and the ability to accommodate a plastic inner liner. More particularly, it is concerned with a bag having a closure in which preferably one panel and the adjoining sides are double folded and the other panel is lapped over the double fold and adhesively secured, thus providing a stronger seam and sift proof corners. Additionally, a valve may be inserted between the tube panels prior to folding which allows field packing and emptying. Further, plastic inner liner may be easily incorporated providing a moisture barrier for the contents of the bag.
2. Description of the Prior Art
In the packaging industry many types of bag closures are used, but two main types have gained widespread acceptance. However, as will be seen, each of these two types of bags have associated problems. The first type, the sewn bag, is simply a closure where tape is placed over the end of the bag and the tape and the bag are transversely sewn. The sewn closure has significant shortcomings, not only in the expense of the sewing operation, but more importantly, lateral forces imposed on the closure tend to concentrate along the sewn seam. The concentration of lateral stress forces along a transverse line often results in burst seams, as for example when a bag is dropped. The sewn closure is also difficult and expensive to valve.
The second type of bag, the pinched bottom closure, is stronger than the sewn closure, but is deficient in a number of other respects. A particular problem with the pinched type closure is that it must be made using stepped end tubes which are ore expensive to manufacture than flush cut tubes. Additionally, the top and bottom of the bag require a great deal of solid spot pasting, especially in a multiwall type container. Although a pinch bottom bag may be valved, it is a process involving a large amount of spot pasting, thus increasing the cost.
A number of bags with folded closures have been proposed in the past. In general, however, these closures have not met the needs of the packaging industry, because of their additional expense in manufacture or insufficient strength of the closure. Patents illustrating these prior closures includes U.S. Pat. Nos. 3,526,354, 2,429,505, 3,910,488, and 3,927,825.